The "hands" of industrial robots typically comprise a pair of spaced, opposed gripping jaws, with one or both of the gripping jaws pivotally mounted to a base. One or both of the gripping jaws is also connected to an actuating mechanism, such as the piston rod of a hydraulic cylinder-piston assembly. Thus, displacement of the movement of the piston rod resulting from displacement of the piston within the cylinder provides the activating force for opening or closing the gripping jaws.
U.S. Pat. No. 3,945,676, issued to Asamoto, discloses a gripping device for use in an industrial robot or manipulator including a pair of clamp arms mounted on the base plate and connected to an activating rod through a single toggle mechanism comprising a pair of links each pivotally mounted at one end for concurrent movement to the activating rod, with the free end of each link pivotally mounted to each of the clamp arms respectively, providing for a locking closure of the clamping arms upon extension of the activating rod.
The employment of a toggle mechanism in the Asamoto device provides a simple locking mechanism with a degree of mechanical advantage. However, existing robot gripping mechanisms often lack sufficient gripping forces to safely secure relatively heavy workpieces which often have large deviations in size from piece to piece.